A known example of a conventional surface plasmon resonance fluorescence analysis device (also to be simply referred to as a “fluorescence analysis device”) is described in Patent Document 1. In this analysis device, by generating surface plasmon resonance in a metal film deposited on a prism, an electric field (intensified electric field) that is intensified is formed in the vicinity of the surface of the metal film, and a specimen is detected with both high sensitivity and high accuracy by utilizing this intensified electric field.
More specifically, as indicated in FIGS. 6 and 7, this fluorescence analysis device is provided with a prism unit 110 on which a metal film 112 is formed, a light source 120 that emits a light beam α towards the prism unit 110, a light receiving unit 130 that measures the light beam α reflected by the prism unit 110, and fluorescence detection means 140 for detecting light (fluorescence) based on an intensified electric field in the vicinity of the metal film 112.
The prism unit 110 is provided with a triangular prism (to be simply referred to as a “prism”) 114, a metal film 112 deposited on a prescribed surface 114b opposing the vertical angle of the prism 114, an antibody solid layer film 113 deposited on the surface 112a of the metal film 112 (on the opposite side from the prism 114) and in which an antibody that captures a specific antigen in a specimen (sample solution) is immobilized on the surface thereof, and a flow path member 117 having a flow path 116 enabling the specimen to flow while contacting the surface of the antibody solid layer film 113.
In this prism unit 110, the prism 114 causes the light beam α emitted from the light source 120 to enter the prism 114 from one inclined surface (incident surface) 114a thereof, and the light beam α reflected by the metal film 112 provided on a prescribed surface 114b is emitted to the outside from the other inclined surface (emission surface) 114c. More specifically, the light beam α that has entered the prism 114 is totally reflected from the back side of the metal film 112 (side of the prism 114) at the surface 112a of the metal film 112, and is emitted outside the prism 114 from the emission surface 114c. 
The light source 120 emits the light beam α towards the incident surface 114a of the prism 114. This light source 120 is composed so as to be able to change an angle of incidence θ of the light beam α relative to the metal film 112. The light receiving unit 130 receives the light beam α emitted outside the prism 114 from the emission surface 114c of the prism 114 as a result of being reflected by the metal film 12, and measures the intensity thereof. The fluorescence detection means 140 is arranged at a location opposing the metal film 112 with the flow path 116 interposed therebetween, and detects fluorescence of a fluorescent substance excited by an intensified electric field formed in the vicinity of the surface of the metal film 112.
Testing of a specimen is carried out in the manner described below in this fluorescence analysis device 100.
The fluorescence analysis device 100 determines the angle of incidence θ of the light beam α relative to the metal film 112 for forming an intensified electric field in the vicinity of the surface of the metal film 112 (and more precisely, the angle of incidence θ of the light beam α that enters the surface 112a of the metal film 112 from the back side 112b) prior to allowing a specimen to flow through the flow path 116. More specifically, the light beam α is emitted from the light source 120 while changing the angle of incidence θ of the light beam α relative to the metal film 112. At this time, the light beam α reflected by the metal film 112 is received by the light receiving unit 130, and the intensity thereof is measured. As a result, a resonance angle (SPR angle) θ1 is determined which is the angle of incidence relative to the metal film 112 at which surface plasmon resonance is generated in the metal film 112 (see FIG. 8). More specifically, the angle of incidence relative to the metal film 112 at which the intensity of reflected light is the lowest (namely, the angle of incidence at which reflectance is lowest) becomes resonance angle θ1. Here, as shown in FIG. 8, a shift occurs between the resonance angle θ1 at which surface plasmon resonance is generated in the metal film 112, and an angle of incidence θ2 of the light beam α relative to the metal film 112 at which the intensified electric field reaches a maximum (maximum intensified electric field angle). Namely, the resonance angle θ1 and the maximum intensified electric field angle θ2 do not coincide. Consequently, the fluorescence analysis device 100 determines an angle of incidence (measuring angle) θ3 when testing a specimen by adjusting (normally by ±05°) a prescribed angle from the determined resonance angle θ1.
The emitting direction of the light source 120 is adjusted so that the angle of incidence of the light beam α relative to the metal film 112 becomes the measuring angle θ3. As a result, the intensified electric field formed in the vicinity of the surface 112a of the metal film 112 (in the vicinity of the metal film 112 on the side of the flow path 116) roughly reaches a maximum. The specimen is then allowed to flow through the flow path 116 when in this state.
When the specimen flows through the flow path 116, a target substance (specific antigen) in the specimen is captured by antibody immobilized on the antibody solid layer film 112a by an antigen-antibody reaction. By then allowing a fluorescently labeled antibody to flow through the flow path 116, only the portion where antigen has been captured is labeled with the fluorescent substance. This labeled fluorescent substance emits light as a result of being excited by the intensified electric field formed in the vicinity of the surface of the metal film 112. As a result of this fluorescence being measured by the light receiving unit 130, the amount of antigen that has reacted in the fluorescence analysis device 100 can be measured with high sensitivity and high accuracy.
The amount of the angular shift between the resonance angle θ1 at which surface plasmon resonance is generated in the metal film 112 and the maximum intensified electric field angle θ2 at which the intensified electric field in the vicinity of the surface of the metal film 112 reaches a maximum is determined by various parameters. Thus, if some of the parameters differ, since this causes a change in the amount of shift between the resonance angle θ1 and the maximum intensified electric field angle θ2, even if the measuring angle θ3 is determined by accurately determining the resonance angle θ1 for each test, there are cases in which the intensified electric field formed in the vicinity of the surface of the metal film 112 does not reach a maximum. Namely, variations occur in the magnitude of the intensified electric field for each test in the fluorescence analysis device 100. Consequently, variations attributable to the fluorescence analysis device 100 may occur in measurement results even when testing the same specimen.    Patent Document 1: Japanese Patent Publication No. 4370383